Free piston machine



May 26, 1964 A, BRAUN FREE PISTON MACHINE Filed Nov. 21, 1960 6 Sheets-Sheet 1 l |||||||||||||l l May Z6, 1964 A. BRAUN FREE: PIsToN MACHINE 6 Sheets-Sheet 2 Filed NOV. 2l, 1960 May 26, 1964 A. BRAUN 3,134,372

FREE PISTON MACHINE Filed Nov. 2l, 1960 6 Sheets-Sheet 3 www,

May 26, 1964 A. BRAUN 3,134,372

l FREE PIsToN MACHINE Filed Nov. 21, 1960 6 Sheets-Sheet 4 A. BRAUN FREE PISTON MACHINE 6 Sheets-Sheet 5 May 26, 1964 Filed Nov. 21, 1960 d Y E 1| .had //Wmnm, mwmmmmm mm May 26, 1964 A. RAUN 3,134,372

FREE PISTON MACHINE Filed Nov. 21, 1960 6 Sheets-Sheet 6 /42/43 d/257 244 United States Patent Ofi ce l 3,134,372 Patented May 26, 1964 3,134,372 FREE PISTGN MACHINE Anton Braun, Kingston, Ontario, Canada Filed Nov. 21, 1969, Ser. No. 70,650 17 Claims. (Cl. 123-46) This invention relates to free piston machines and is a continuation-impart of application Serial No. 854,912, filed November 23, 1959.

In free piston machines, a pair of stepped pistons work together in opposed reciprocating motion within a common engine cylinder to which, usually on each end thereof, a compressor cylinder is coaxially arranged and in which the larger diameter portions of the stepped pistons work. Depending on the principle according to which such machines work, that is, whether they work with the compresion of the air within the compressor parts during the outward stroke, or during the inward stroke or possiblly during both strokes, it is more or less important, and in certain cases, imperative, to incorporate in a machine a bounce structure. However, conventional bounce structures, particularly in engines of the outward compression type, are subject to several disadvantages. Thus, they usually involve the use of many additional parts, sometimes of relatively complicated form, and they undersirably increase the bulk of the engine.

Furthermore, in usual free piston machines, the pistons, during their reciprocating motion, are supported on working surfaces of the machine. Since the pistons at different loads have different temperatures, they change in size with respect to the size of the cylinders in which they reciprocate. Moreover, the diameters of, for instance, the Diesel portions of the pistons are not the same over their entire lengths. If careful production procedures are applied, the pistons can be machined such that the diameters over their entire lengths at one load condition are fairly equal, but this is not so for other loads. To overcome the problems incident to this problem, so-called wear bands Ihave been employed. These wear bands are attached to the pistons and are made from a material that wears well under the engine conditions. Since, however, such wear bands are still in contact with the hot working cylinder surfaces they are subject to chemical as well as excessive mechanical wear and must be replaced frequently. This problem would be more serious in engines of shorter design than usual since the length of hot contact would be relatively longer.

Another common characteristic of free piston engines is that the thermal load in the combustion or Diesel section is a governing factor in respect of maximum possible efliciency. The thermal load must be in such a range that the piston rings having regard to the lubrication will safely stand the load. There are other problems such as the provision of material for the piston crowns that will withstand the high temperatures in the combustion section, but such problems are less severe and some solutions therefor have been provided such as, for instance, cooling of the piston crowns. The usual way of dealing with piston rings and lubrication and the corresponding wear problems is to improve the contacting materials, which, in many cases, results in higher costs, or to improve the ulbricants or utilize new lubricants that will stand the higher thermal loads associated with higher efficiency, a step which also results in higher costs. There is, therefore, an economical limit in respect of the maximum eiciency at which an engine may be operated, even in those cases where the fuels and engine cycles used permit such operation of engines at higher efficiency.

In high sped engines, it is also dili'icult to find suiiicient space particularly for the compressor delivery valves. It is partly for this reason that the velocities in these valves are very high which results in a lower life expectancy for the valves.

It is a general object of this invention to provide a free piston machine of simplified construction, of more compast form, and of improved operating eiiiciency.

A more specific object is to provide a ringless piston structure for free piston engines having a supporting means therfor involving absence of mechanical contact between the pistons and cylinder in the combustion section thereof whereby lubrication'and cooling means are avoided, the clearance betwen pistons and cylinder being kept to a minimum whereby undesirable leakage is eliminated.

Another object is to provide a bounce structure for free piston machines which avoids the need of additional parts and which thereby improves the engine design whereby its efficiency is increased, its construction is simplified and its operation is rendered safer.

Another specific object is to provide piston assembly bearings that are remote from the hot working surfaces and can therefore be kept at very safe temperatures.

Another object is to provide a free piston machine wherein the thermal load problem is avoided in an inexpensive manner resulting in a less costly, safer, more eticient and lighter enginer.

Another object is to provide a free piston engine having a compact valve arrangement with consquent space conservation and resulting in safer operation.

Other objects, details and advantages will become apparent from the following description, with particular reference to the accompanying drawings, in which- FIGURE 1 is a sectional side elevation of a free piston machine in accordance with the invention,

FIGURE 2 is a partial sectional elevation of a modified form of machine,

FIGURE 3 is a section on line 3-3 of FIGURE l,

FIGURES 4 to l2 inclusive, are partial sectional elevations of other modified forms of free piston machines in accordance with the invention,

FIGURE 13 is a sectional side elevation of a modified form of engine,

FIGURE 14 is a sectional side elevation of still another modified form of engine,

FIGURE 15 is a sectional side elevation of another modified form of engine,

FIGURE 16 is a sectionon line 16-16 of FIGURE l5,

FIGURE 17 is a section on line 17--17 of FIGURE 15,

FIGURE 18 is a side elevation, partly in section of another form of engine, and

FIGURE 19 is a section on line 19-19 of FIGURE 18.

Referring to FIGURES 1 and 3, the free piston machine illustrated has a pair of compressor cylinders 1 which are supported in spaced axial alignment as by open frame members 2. A power or combustion cylinder 3 of substantially smaller diameter than that of cylinders 1 is arranged between cylinders 1 in axial alignment therewith and with its end portions extending through the inner open ends of cylinders 1. The cylinder 3 is supported on spider frames 4 each comprising a ring 5 fixed to the inner end of a cylinder 1 and a plurality of inclined spider arms 6.

A pair of piston assemblies 7 are mounted for reciprocating in cylinders 1 and 3. Each piston assembly comprises a compressor piston 8 and a power piston 9. The compressor piston comprises a ring 10, a hub 11 fixed to a guide shaft 12, and an intermediate frusto-conical portion 13. The power piston 9 is open at its outer end and has a closed inner end wall 14 to which the end of guide shaft 12 is fixed.

The guide shaft 12 is reciprocally mounted in a bearing 15 carried by a compressor cylinder head 16 and a bearing 17 carried by a cylindrical member 18 which is #3J mounted on the spider frame and in the modiiication shown, extends into the portion of cylinder 3 lying within the compressor cylinder 1. It will be observed that the bearing 17 is shown as being located in the inner end portion of the cylindrical member 18.

The cylindrical member 1S has an outer cylindrical surface 19 which is in spaced relation to the interior surface of cylinder .3 to provide a space for reception of the skirt of power piston 9 and that in the outward po-sition of the latter piston there is an annular chamber Ztl between the internal piston surface and the surface 19 of the cylindrical member. The cylindrical member 18 has a generally conical recess 21 for reception of a complementarily shaped portion of hub 11 of the compressor piston. Furthermore, the hub 11 has a generally conical recess 22 for reception of a complementarily shaped portion of the bearing 15.

In the embodiment shown, each compressor piston is provided with piston rings 23 on the ring 1l) and each power piston is provided with piston rings 24.

The combustion cylinder`3 is provided with a plurality of air intake ports 25 communicating with a passage 26 formed by an annular member 27 and a conduit 23. Conduit 2S communicates through openings 29 with an air receiver chamber 30 formed in each cylinder head 16. As shown, each cylinder head has a cylindrical side wall 31 constituting a continuation of the side wall of cylinder 1, an end wall 32, and an inner wall 33 of frusto-conical form. The cylinder head thus provides a recess 34 for reception of the conical portion of compressor piston 8. Chamber 3) communicates with the interior of compressor cylinder 1 through conventional one-way valves 35 in wall 33 which open on the outward stroke of piston 8 and are closed on the inward stroke thereof.

Combustion cylinder 3 is also provided with a plurality of exhaust ports 36 which communicate with an exhaust passage 37 formed by annular member 3S and exhaust pipe 39. The fuel injection nozzle of the combustion cylinder is indicated at 4t).

At the end of the outward stroke of the compressor pistons 8, there is a compressor clearance space 41 between each piston portion 13 and the wall 33.

Each compressor cylinder 1 is provided with a plurality of air intake ports 42 each controlled by a conventional one-way valve 43 which opens during the inward stroke of the piston S and is closed during the outward stroke thereof.

Installation and servicing of valves 35 may be eiected by access openings 44 in wall 32 provided with closure plates 45.

In operation, air ente-rs the compressor cylinders 1 through intake ports 42 during the inward stroke of pistons S; during the subsequent outward stroke of pistons 8, such air will be compressed in cylinders 1 and, after having reached its delivery pressure, discharged through valves 35 into receiver chambers 3i?. The air then passes through openings 29 and reaches ports 25 through passage 26. Near its outermost position, one piston 9 opens exhaust ports 36 and, after the exhaust gases have completed their blow down process, the other piston 9 opens intake ports 25 through which the air that was compressed during that same outward stroke of the piston assemblies now enters combustion cylinder 3 for scavenging and recharging.

During their outward strokes, the piston assemblies have stored sutlicient return or bounce energy in chambers 20 as well as in the compressor clearance spaces 41 to force them back into their innermost positions thus doing corresponding work during the thermal compression stroke inside cylinder 3 between pistons 9, as well as the friction work and the work on the atmosphere by the inner surfaces of pistons 8. Towards termination of the inward stroke, the air in combustion cylinder 3 between pistons 9 reaches a very high pressure and temperature and fuel is injected through nozzle 4t). Due to the resultant combustion and expansion of the combustion gases as well as the work effected by the atmosphere on the confronting surfaces of pistons 8, the piston assemblies are forced apart from one another and the available work from this expansion or power stroke will be used up firstly by compressing and delivering the air inside each compressor cylinder 1 between the outside surface of compressor piston 8 and the wall 33 of the cylinder head, secondly byv the friction between the moving and the stationary parts of the engine, and thirdly by the air or gas compressed in bounce chambers 2l). After all the work available on the outward stroke of piston assemblies is distributed in this manner, the piston assemblies have reached their outermost positions and the whole cycle begins again, the stored up return or bounce energy forcing the piston assemblies again into their innermost positions for the next Diesel compression and compressor intake stroke.

It will be apparent that the structure described provides the usual bounce action of outward compression engines with separate bounce chambers, but in this case without the need of special bounce pistons or bounce cylinders. The provision of the cylindrical members 18 in association with pistons 9 provides a compact and effective bounce structure thus eliminating the need for bounce pistons and cylinders of conventional or like nature.

Moreover, in the structure described, the piston assemblies are guided in bearings 15 and 17 that are quite remote from the thermodynamic Working surfaces of the compressor pistons il, the power pistons 9, and the hot wall surfaces of cylinders 1 and 3. Thus, the bearings 15 and 17 may be kept at safe operating temperatures. The outstanding advantage of this arrangement is that piston seizing due to thermal expansion is eliminated since the clearances between the pistons and the complementary surfaces of the cylinders can be made so large that at no one load will mechanical contact occur. It will also be apparent that water, oil or similar cooling means for the guide shafts and bearings may readily be incorporated in the structure. Since the bearings 15 and 17 positively seal the ends of the cylinders 1 and 3, no gas or lubricant can leak out of the cylinder ends. Thus, instead of the usual lost oil lubrication system, a simple recirculating lubrication system may be employed resulting in easier and better lubrication of the diesel section.

Another advantage of the arrangement resides in the fact that, near the innermost position of the piston assemblies the pressure between the pistons 9 is very high, i.e., higher than that in bounce chambers 20, whereas at a position between the innermost and outermost positions of the piston assemblies the pressure in bounce chambers Ztl irst reaches a level equal to the pressure between pistons 9 and then during the remaining portion of the outward stroke the pressure in the bounce chambers will rise to values considerably in excess of the pressure between the pistons 9. Since pressure in the bounce chambers at certain periods, if not at all times, is at least as high as the compressor or delivery pressures, gas or air from the bounce chambers will always leak out of it and if this is always replaced a very desirable venting of the bounce chambers takes place. Moreover, such small loss does not represent a full loss since part of the lost energy may be regained in any expansion machine, such as a turbine, which is connected to the free piston engine.

Another important structural characteristic of the machine described is that the arms 6 of the frame 4, the piston portions 13 of compressor pistons 8, and the wall 33 of the receiver chamber 30 are disposed in inclined relation to the axis of the engine. As shown, the angle of inclination of these elements is approximately uniform. The purpose of this arrangement is twofold. Firstly, it makes it possible to build a substantially shorter engine. Secondly, it is possible, by selecting the angle of inclination such that the diameter that passes through the centers of valves 35 is increased to a value of which the circumference of the corresponding circle is a multple, say 1.5 times the value, of the circumference that the same size of valves 35 would require if placed vertically within the same overall size of engine, to install 1.5 times the number of valves 35. This is of considerable importance since then 1.5 times the free valve area is available to discharge the air and since the pressure losses decrease with about the second power of the inversed area available in the valves, not only is the overall eiciency of the engine increased 'but the life expertancy of the valves is increased with resultant prolonged and safer engine operation.

FIGURE 2 illustrates an engine which is similar in all respects to that shown in FIGURE l but in which no piston rings are employed "on pistons 8 and 9. Such a structure takes full advantage of the features of construction hereinbefore set forth. The outer surfaces of rings 10 of pistons 8 may be provided with labyrinths. The skirts of pistons 9 may also be provided with labyrinths which in high speed engines, however, and in View of the extremely smal clearance possible, and since now leakage would occur outside the engine, might be avoided. If this sealing feature and the balancing effect of the pressure were not present, it would be very undesirable to eliminate use of piston rings since the leaking gas would either leak into the atmosphere (which would mean a loss and contamination of the surrounding area) or it would leak into chambers and other areas of the engine where its presence is undesirable. Moreover, with unrestricted ilow of gas, the gas leakage would be undesirably large and the resulting high rate of ow of the hot gas would deteriorate pistons and cylinders badly.

The advantages of yemploying ringless pistons in free piston engines are of great importance and may be summarized as follows:

(a) Since there is no mechanical contact between the pistons and the cylinder walls and no piston rings in contact with the cylinder walls, there is no necessity to lubricate either the combustion or compressor section of the engine, and as a consequence no necessity for cooling.

(b) Since the provision of cooling means in the combustion section is unnecessary because of the absence of mechanical contact between pistons and cylinder, losses as a result of cooling are avoided. The efficiency gain as a result of the saving in cooling could, however, be offset by leakage if the ,'clearance were not kept to a minimum. The means whereby such minimum clearance is accomplished is a common characteristic of the structures described in all the modifications herein.

(c) Because such lubrication is unnecessary, the common thermal load barrier in respect of piston rings and lubricants does not now exist and therefore compression ratio can be raised.

(d) With raising of the pressure in all chambers, the size of the engine, and particularly of the compressor pistons, is decreased with a consequent considerable increase in cyclic frequency, which reduces any sealing problem between pistons and cylinders since the time available for gas to flow during any one cycle is decreased to an extremely low value.

(e) Instead of having to cut ports into a cylinder, only a circular `open ring space is necessary since no piston rings are present. When piston rings are employed, it is, of course, necessary to cut ports into the cylinders whereby bridges between the ports are provided to guide the piston rings past the ports.

Also the arrangement of the delivery valves is of considerable significance since at the higher speed of ringless piston engines it is substantially essential to provide for increased 'valve area and longer valve life.

With normal valve arrangements, the gains due to insulated (instead of cooled) liners and due to higher compression ratios could again be easily olfset.

FIGURE 4 illustrates an arrangement for providing flow of air from air receiver chamber 30 of compressor cylinder head 16 to bounce chamber 20 if at the innermost position of the piston assemblies pressure in the bounce chamber is below that in chamber 30. The arrangement comprises an axial bore 46 in guide shaft 12 having a port 47 at its inner end communicating with the interior of piston 9 adjacent its end wall 14 or in any other desirable location and thus with chamber 20 in the innermost or any other desirable position of the piston assembly. The bore 46 also communicates with a chamber 48 formed by a cup 48a mounted on end Wall 32 and which is connected to chamber 30 by a bore 49. A check valve 50 permitting the desired flow is provided in the bore.

FIGURE 5 shows an auxiliary bounce structure for use when additional bounce energy is required, such structure being conveniently formed to serve as an outer guide bearing for the piston assembly as well as a bounce means. It comprises a cylindrical rearwardly extending member 51 on the piston assembly slidably received in a hollow cylindrical bearing member 52 carried by the outer wall 32 of the cylinder head.

FIGURE 6 illustrates another type of auxiliary bounce structure which may be readily incorporated in the engine of the present invention. A hollow cylindrical member 53 is mounted on a tubular extension 54 of end Wall 32 of the cylinder head and extends through. such extension with its side wall in spaced relation thereto. The inner end wall 55 of member 53 constitutes a bearing for the guide shaft 12. The compressor piston 8 has a rearwardly extending tubular portion 56 which receives the member 53. Thus, an auxiliary bounce chamber 56a is provided between the inner end surface 55 of member 53 and the bottom wall of tubular portion 56.

In the modifications' thus far illustrated, the cylinder head has been shown as a separate member attached to the outer end of the compressor cylinder. FIGURE 7 illustrates a modified form of structure wherein a compressor cylinder 57 and cylinder head 58 are formed as a one piece member, and the ring 5 of frame 4 constitutes a means for concentrically aligning this one piece member with a center frame 59.

FIGURE 8 illustrates a modification wherein, instead of arms 6 in frame 4, a closed frusto-conical wall 60 is provided. Such a structure provides a closed chamber 61 between frame 4 and compressor piston 8 which can be employed as a negative bounce chamber. Thus, on the outward stroke of the piston assemblies, vacuum is drawn in chambers 61 of the engine and the bounce action is thereby supported. An air vent valve or valves 62 may be provided in wall to assure that any air which has leaked into the chambers can escape from the chambers at the end of the inward stroke of the piston assemblies.

FIGURE 8 also illustrates a structural modification which permits removal of the cylinder head and compressor piston from the engine while the power piston 9 and frame 4 remain in place. To this end, a hollow guide shaft 63, instead of guide shaft 12, is provided, such shaft being attached to piston 9 by means of a tie rod 64 which has one end xed to piston 9 and which extends axially through the shaft 63. Washer 65 and nut 66 or other suitable means, iix the other end of the tie rod to the outer end of the shaft. It will be apparent that, on removal of the washer 65 and nut 66, the shaft 63 with cylinder head 16 and compressor piston 8 may be removed from the engine while piston 9 and frame 4 remain in place.

FIGURE 9 illustrates a simple means for cooling the crown of piston 9. Instead of guide shaft 12 a hollow shaft `67 is employed, the interior of which communicates with a chamber 68 in the piston crown. A tube 69 extends axially through the hollow shaft 67 in spaced relation thereto to provide a passage between the tube and shaft. Thus, a cooling liquid may be circulated through tube 69 into chamber 6 8 and out through passage 70, as indicated by the arrows. Obviously, the direction of flow of the cooling liquid may be reversed, if desired.

FIGURE illustrates a simple manner of incorporating a cooling system in the structure of FIGURE l. As shown, an annular passage 71 is formed in spigot member 18 with an inlet duct 72 and an outlet duct 73 for cooling liquid. Bearing is also provided with an annular passage 74 with an inlet duct '75 and an outlet duct 76 for cooling liquid.

FIGURE ll illustrates a porting arrangement yfor cylinder 3. In this arrangement, the outer end portion 77 of the cylinder may be formed as a separate part spaced from the main portion thereof. A ring 78 surrounds the space between the parts and ports 79 are provided therein. The ports 79 may be only four in number and the intervening portions 89 of the ring may be quite narrow whereby substantially the entire space between the portion 77 of the cylinder and the main portion thereof may be utilized for flow. Furthermore, the ring 78 may be employed as the supporting connection for the cylin- -der portion 77. It will be understood that machines utilizing the arrangement described will use no piston rings.

Referring to FIGURE 12, a machine providing a two stage bounce effect is therein illustrated, such machine generally combining the structures of FIGURES 4 and 6. As shown, air is drawn from compressor receiver chamber 3) through a tube 81 to supercharge a first stage bounce chamber S2. Through a check valve 83 air from chamber 30 will enter bounce chamber S2 when the piston assembly is in its innermost position. On the outward stroke, this air is compressed to a higher pressure than that in the compressor receiver chamber 30. Through a check valve 84 air at this high pressure will enter a chamber 85 formed by the interior of member 53 and a cover plate 86. In the innermost position of the piston assembly again the air of this latter high pressure will enter through bore 46 in bar 12 and check valve 50. Annular chamber now acts as a second stage bounce chamber. In this second stage bounce chamber the compression on the outward stroke will thus start at an unusually high bounce pressure. For the same bounce energy requirements, this will result in a lower maximum pressure in chamber 29 in the outermost position of the piston assembly, thus exerting a lesser strain on the elements concerned.

Referring to FIGURE 13, S6 is a generally cylindrical casing having end walls S7. Mounted within the casing is a cylindrical member 88 arranged in concentric spaced relation thereto to provide a passage 89 therebetween. The end portions of member dit constitute compressor cylinders 911 defined by annular frame members 91. Members 91 carry a combustion cylinder 92 axially disposed between cylinders 90. Extending axially through cylinders 90 and 92 is a shaft 93 having its ends supported in end Walls S7. Reciprocally mounted on shaft 93 are a pair of piston assemblies 94 each comprising a compressor piston 95 for reciprocation in a cylinder 90 and a combustion or power piston 96 for reciprocation in cylinder 92. Each piston assembly has bearings 97 disposed adjacent each end thereof for contact with shaft 93. The combustion cylinder is provided with air intake ports 98 communicating with passage 39 and exhaust ports 99. Each compressor cylinder 9@ has a plurality of air intake ports 100 in the end Wall S7 controlled by conventional one-Way valves 191 and a plurality of air outlet ports 102 leading to passage 89 and controlled by conventional one-way valves 103.

The shaft 93 may be centrally supported by a spider or like support 104. Conventional fuel injection means (not shown) are provided and may be associated with the central support.

Since the piston assemblies are fully supported on the shaft throughout their lengths, the possible deflection of the piston support shaft 93 relative to cylinder 92 is reduced to a minimum. Thus, it is possible to provide a clearance of minimum degree between the peripheries of pistons 96 and the walls of cylinder 92. Such clearance need not be greater than 3%,00 of the diameter of power cylinder 92 and may be considerably less. To prevent passage of gas from the combustion cylinder to the bounce chamber, sealing means may be provided between the confronting surfaces of each piston 96 and cylinder 922.

Referring to FIGURE 14, 1115 is a cylindrical casing and 196 are compressor cylinders axially arranged therein. The outer end of each cylinder 166 is supported in a generally conical frame member 107 carried by the casing and the inner end of each cylinder is supported on a centrally disposed generally cylindrical frame member 168. A passage 1119 is formed betwen casing and cylinders 166 and frame member 10S, which may be integral with casing 1G15 or in fixed spaced relation therewith.

A combustion cylinder 110 is axially supported between cylinders 106 by means of a pair of webs 111 carried by frame member 1% and each engaging an outwardly projecting extension 112 of the cylinder 119. In the form shown, each extension 112 projects into a respective compressor cylinder 1%.

Axially arranged within the casing and extending axially through the cylinders 106 and 110 is a shaft 113 having its ends supported in brackets 11dcarried by frame members 107.

Reciprocally mounted on shaft 113 are a pair of piston assemblies 115 each comprising a sleeve 116 each end of which is provided with a bearing 117 for contact with the shaft. Fixed to each sleeve intermediate the ends thereof is a compressor piston 113 which has an outwardly extending conical portion 119 and a reversely or inwardly extending conical portion 120 the periphery of which cooperates with the respective cylinder 196. Such periphery may be provided with a piston ring 121 or the like for contact with the cylinder Wall. Each piston assembly also comprises a power piston 122 having an inner end wall 123 fixed to the inner end of sleeve 116 and a skirt 124. Piston 122 is free from contact with the wall of the combustion area of cylinder 11@ but the outer end of the skirt, which reciprocate in extension 112, may be provided with a piston ring 125 or the like.

The outer end of each sleeve 116 is supported for reciprocation in a conical web 126 carried by frame member 107. In the modification shown, it will be apparent that the reverse conical formation of member 107 and supporting web 126 permits reception therebetween of the conical portions 119 and 129 of the compressor piston 118. Web 126 may be provided with a piston or sealing ring 127 for engagement with the sleeve. The inner portion of sleeve 116 is supported in an inwardly directed tapered or conical member 136 carried by the combustion cylinder extension 112. Member 136 has a piston or sealing ring 137 for engagement with the sleeve. It will be apparent that the member 136 corresponds to the cylindrical member 18 of FIGURE l and provides a conical recess 138 for reception of the conical portion 119 of the compressor piston. The compressor piston has a one-way valve 139 in portion 120 thereof.

Each end of the casing 10S may be provided with a protective cover 12S which enclosese the projecting frame 107 and bracket 11d.

The end of each compressor cylinder 106, as constituted by the frame member 197 and the web 126, is provided with air intake ports 129 controlled by conventional oneway valves 130, and air drawn in through such ports on the inward stroke of the piston is discharged through ports 131 in the cylinder 196 and controlled by conventional one-way valves 132 into passage 109 0n the outward stroke of the piston. Aair from passage 109 is charged into the combustion cylinder 11) through ports 133. The combustion cylinder is provided with exhaust ports 134 as well as conventional fuel injection means (not shown). Preferably, the outer surface of the combustion cylinder is insulated by bands of insulation 135. Each piston extension 112 may be provided with a chamber 140 for reception of cooling liquid.

Referring to FIGURES 15, 16 and 17, 141 is a generally cylindrical casing having a cylindrical member 142 arranged therein to provide an annular passage 143 therebetween. As shown, member 142 is cast integrally with casing 141.

Mounted on each end of member 142 is a compressor cylinder 144 the outer end of which is closed by a wall 145 having an outwardly projecting conical portion 146 and a reversely directed inwardly extending conical portion 147.

A combustion cylinder 148 is carried by webs 149 on the member 142 the outer ends of cylinder 143 extending axially into compressor cylinders 144.

A pair of piston assemblies 150 each comprise a shaft 151 reciprocally mounted in cylinder wall portion 147 and a cylindrical member 152 carried by member 142. A compressor piston 153 and a combustion piston 154 are mounted on shaft 151, the arrangement thereof with relation to the compressor and combustion cylinders being generally similar to the embodiment of FIGURE l.

Conventional one-way valves 155 in walls 145 permit passage of air into the compressor cylinders on the inward stroke of the piston assemblies and one-way valves 156 permit passage of air from the compressor cylinders to the passage 143. Passage 143 is divided into branches 157 leading to air charging ports 158 in the combustion cylinder. The combustion cylinder has exhaust ports 159 leading to exhaust member 160.

Referring to FIGURES 18 and 19, a unitary casing member 161 has pairs of arcuate passages 162 leading from compressor cylinders 163 through valve controlled ports 164 for conducting charging air to the combustion cylinder 165 through ports 166. The basic elements of the engine including compressor cylinder end walls 167 and piston assemblies 163 are closely similar to the corresponding elements in the modification of FIGURES 15, 16 and 17. It will be appreciated that the arrangement shown permits a somewhat flattened engine as shown in FIGURE 19, and that the cylinders are open to atmosphere through openings 169 and 170.

It will be apparent that, in each of the modifications described, mechanical contact between the combustion piston and its cylinder in the combustion section thereof may be avoided, thus attaining the advantages heretofore set forth. Moreover, in each of the modilications described, the piston assembles are positively supported at all times during operation thereof whereby they maintain true axial alignment. Thus, as previously indicated, the clearance between the piston and cylinder may be kept to a minimum (not substantially greater than lOO of the power cylinder diameter) whereby excessive leakage is avoided and very high efficiencies can be achieved.

I claim:

1. A free piston machine comprising a rigid frame including a pair of axially aligned compressor cylinders and a combustion cylinder between said compressor cylinders, a pair of piston assemblies each having a compressor piston disposed for reciprocation in one of said compressor cylinders and a power piston of a diameter not larger than that of said compressor piston disposed for reciprocation in said combustion cylinder, each said power piston having a crown, and means supporting said piston assemblies for reciprocal movement comprising two guide shaft parts axially arranged with respect to said piston assemblies, a pair of spaced bearings engaging each said guide shaft part for reciprocal movement thereof in said bearings, a separate support fixed to said frame and carrying each said bearing, each said piston assembly being fixed to one of said guide shaft parts with said compressor piston being disposed between said pair of spaced bearings, each said guide shaft part extending through one of said compressor pistons and into the crown of one of said power pistons, and a cylindrical member projecting axially into each end of said combustion cylinder, each said cylindrical member being carried by one of said supports and having mounted therein one of said bearings, each said cylindrical member having an exterior cylindrical surface in radially spaced relation to the opposed cylindrical interior surface portion of said combustion cylinder to provide an annular chamber therebetween, each said power piston having a skirt reciprocally receivable in one of said annular chambers to compress air therein, each said annular chamber thereby constituting a bounce chamber.

2. A free piston machine as defined in claim 1, including a cylinder head mounted on the outer end of each said compressor cylinder, another of said bearings being mounted in each said cylinder head.

3. A free piston machine comprising a rigid frame including a pair of axially aligned compressor cylinders and a combustion cylinder between said compressor cylinders, a pair of piston assemblies each having a compressor piston disposed for reciprocation in one of said compressor cylinders and a power piston of a diameter not larger than that of said compressor piston disposed for reciprocation in said combustion cylinder, each said power piston having a crown, and means supporting said piston assemblies for reciprocal movement comprising two guide shaft parts axially arranged with respect to said piston assemblies, a pair of spaced bearings engaging each said guide shaft part for reciprocal movement thereof in said bearings, a separate support fixed to said frame and carrying each said bearing, each said piston assembly being fixed to one of said guide shaft parts with said compressor piston being disposed between said pair of spaced bearings, cach said guide shaft part extending through one of said compressor pistons and into the crown of one of said power pistons, and a cylindrical member projecting axially into each end of said combustion cylinder, each said cylindrical member being carried by one of said supports and having mounted therein one of said bearings, each said cylindrical member having an exterior cylindrical surface in radially spaced relation to the opposed cylindrical interior surface portion of said combustion cylinder to provide an annular chamber therebetween, each said power piston having a skirt reciprocally receivable in one of said annular chambers to compress air therein, each said annular chamber thereby constituting a bounce chamber, a cylinder head mounted on the outer end of each said compressor cylinder, another of said bearings being mounted in each said cylinder head, each said cylinder head having an air receiving chamber therein, each said air receiving chamber having a frusto-conical wall separating said air receiving chamber from the interior of one of said compressor cylinders, and a plurality of one-way valves in each said frusto-conical wall permitting passage of air into said compressor cylinders from said air receiving chambers on the inward stroke of said piston assemblies.

4. A free piston machine as defined in claim 3 including a cylindrical casing surrounding said compressor cylinders in spaced relation thereto and forming an annular passage therebetween, valve controlled air discharge ports leading from each of said compressor cylinders to one of said annular passages, said combustion cylinder having air charging ports therein, and each said annular passage having a branch passage leading to said air charging ports.

5. A free piston machine comprising a rigid frame including a pair of axially aligned compressor cylinders anda combustion cylinder between said compressor cylinders, a pair of piston assemblies each having a compressor piston disposed for reciprocation in one of said compressor cylinders and a power piston of a diameter not larger than that of said compressor piston disposed for reciprocation in said combustion cylinder, each said power piston having a crown, and means supporting said piston assemblies for reciprocal movement comprising two guide shaft parts axially arranged with respect to said piston assemblies, a pair of spaced bearings engaging each said guide shaft part for reciprocal movement thereof in said bearings, a separate support xed to said frame and carrying each said bearing, each said piston assembly being fixed to one of said guide shaft parts with said compressor piston being disposed between said pair of spaced bearings, each said guide shaft part extending through one of said compressor pistons and into the crown of one of said power pistons, and a cylindrical member projecting axially into each end of said combustion cylinder, each said cylindrical member being carried by one of said supports and having mounted therein one of said bearings, each said cylindrical member having an exterior cylindrical surface in radially spaced relation to the opposed cylindrical interior surface portion of said combustion cylinder to provide an annular chamber therebetween, each said power piston having a skirt reciprocally receivable in one of said annular chambers to compress air therein, each said annular chamber thereby constituting a bounce chamber, a cylinder head mounted on the outer end of each said compressor cylinder, another of said bearings being mounted in each said cylinder head, one of said bearing supports for each said guide shaft part comprising a member fixed to the inner end of one of said compressor cylinders and to an outer end of said combustion cylinder and having an intermediate section inclined to the axis of said cylinder and extending from said compressor cylinder inner end to said combustion cylinder outer end.

6. A free piston machine as defined in claim 5, each said compressor piston having a major frusto-conical section arranged to overlap said inclined intermediate section in the innermost position of said compressor piston.

7. A free piston machine :comprising a rigid frame including a pair of axially aligned compressor cylinders and a combustion cylinder between said compressor cylinders, a pair of piston assemblies each having a compressor piston disposed for reciprocation in one of said compressor cylinders and a power piston of a diameter not larger than that of said compressor piston disposed for reciprocation in said combustion cylinder, and means supporting said piston assemblies for reciprocal movement comprising guide shaft means having shaft portions each caryring one of said piston assemblies, a first support fixed to said frame and engaging each said guide shaft means for direct support thereof by said frame at one point, and a second support independently fixed to said frame in spaced relation to said first support and engaging each of said guide shaft portions for direct support thereof by said frame in spaced relation to said first point, each said guide shaft portion extending through one of said compressor pistons and into one of said power pistons, said supports carrying said shaft portions at opposite sides of each compressor piston, each said compressor cylinder having a cylinder head mounted on the outer end thereof, each said cylinder head having an air receiving chamber therein, each said air receiving chamber having a frusto-conical wall separating it from the interior of one of said compressor cylinders, and a plurality of one-way valves in each said frusto-conical wall permitting passage of air into said compressor cylinders from sm'd air receiving chambers on the inward stroke of said piston assemblies, each said compressor piston having a major frusto-conical section arranged to underlap one of said frusto-conical walls in the outermost position of said piston assemblies.

8. A free piston machine comprising a rigid frame including a pair of axially aligned compressor cylinders and a combustion cylinder between said compressor cylinders, a pair of piston assemblies each having a compressor piston disposed for reciprocation in one of said compressor cylinders and a power piston of a diameter not larger than that of said compressor piston disposed for reciprocation in said combustion cylinder, each said power piston having a crown, and means supporting said piston assemblies for reciprocal movement comprising two guide shaft parts axially arranged with respect to said piston assemblies, a pair of spaced bearings engaging each said guide shaft part for reciprocal movement thereof in said bearings, a separate support fixed to said frame and carrying each said bearing, each said piston assembly being xed to one of said guide shaft parts with said compressor piston being disposed between said pair of spaced bearings, each said guide shaft part extending through one of said compressor pistons and into the crown of one of said power pistons, a'cylindrical member projecting axially into each end of said combustion cylinder, each said cylindrical member being icarried by one of said supports and having mounted therein one of said bearings, each said cylindrical member having an exterior cylindrical surface in radially spaced relation to the opposed cylindrical interior surface portion of said combustion cylinder to provide an annular chamber therebetween, each said power piston having a skirt reciprocally receivable in one of said annular chambers to compress air therein, each said annular chamber thereby constituting a bounce chamber, a cylinder head mounted on the outer end of each said compressor cylinder, another of said bearings being mounted in each said cylinder head, each said cylinder head having an air receiving chamber therein, each said air receiving chamber having a frusto-conical wall separating said air receiving chamber from the interior of one of said compressor cylinders, and a plurality of one-way valves in each said frustoconical wall permitting passage of air into said compressor cylinders from said air receiving chambers on the inward stroke of said piston assemblies, a casing surrounding said piston assemblies, said casing having a pair of arcuate passages therein, valve controlled air discharge ports leading from each said compressor cylinder to said arcuate passages, said combustion cylinder having air charging ports therein, and each said arcuate passage leading to said air charging ports.

9. A free piston machine comprising a pair of axially aligned compressor cylinders, a combustion cylinder between said compressor cylinders, a pair of piston assemblies each having a compressor piston disposed for reciprocation in one of said compressor cylinders and a power piston of a diameter not larger than that of said cornpressor piston disposed for reciprocation in said combustion cylinder, a cylindrical member projecting into each end of said combustion cylinder, a supporting frame for said cylindrical member and combustion cylinder, each said cylindrical member having an exterior surface in spaced relation to the opposed interior surface portion of said combustion cylinder to provide an annular chamber therebetween, said power piston having a skirt reciprocally receivable in said annular chamber to compress air therein, said annular chamber thereby constituting a bounce chamber.

l0. A free piston machine as defined in claim 9, each said piston assembly having an axial guide shaft, one of said compressor pistons and one of said power pistons being fixed to said shaft, a cylinder head mounted on the outer end of each said compressor cylinder and having a bearing therein supporting said guide shaft, said cylindrical member also having a bearing therein supporting said guide shaft.

1l. A free piston machine as defined in claim 9, each said cylinder head having an air receiving chamber therein, said air receiving chamber having a frusto-.conical wall separating said chamber from the interior of said cornpressor cylinder, and a plurality of one-way valves in said frusto-conical wall permitting passage of air from said compressor cylinder to said chamber on the outward stroke of said piston assemblies.

12. A free piston machine as defined in claim 9, said supporting frame being fixed to the inner end of one of said compressor cylinders and to the outer end of said combustion cylinder and having an intermediate section inclined to the axis of said cylinders and extending from said compressor cylinder inner end to said combustion cylinder outer end'.

13. A free piston machine as defined in claim 9, each said piston assembly having an axial guide shaft, one of said compressor pistons and one of said power pistons being fixed to said shaft, a cylinder head mounted on the outer end of each said compressor cylinder and having a bearing therein supporting said guide shaft, said cylindrical member also having a bearing therein supporting said guide shaft, said supporting frame having an intermediate frame section inclined to the axis of said cylinders and extending from said compressor cylinder inner end to said combustion cylinder outer end, each said cornpressor piston having a maior frusto-conical section arranged to overlap said inclined intermediate frame section in the innermost position of said piston assembly.

14. A free piston machine as defined in claim 9, each said cylinder head having an air receiving chamber therein, said air receiving chamber having a frusto-conical wall separating it from the interior of said compressor cylinder, and a plurality or one-way valves in said frustoconical wall permitting passage of air from said compressor cylinder to said chamber on the outward stroke of said piston assemblies, said rusto-conical section of said compressor piston being arranged to underlap said frusto-conical wall in the outermost position of said piston assembly.

15. A free piston machine comprising a pair or" axially aligned compressor cylinders, a combustion cylinder between said compressor cylinders, a pair or piston assemblies each having a compressor piston disposed for reciprocation in one of said compressor cylinders, a power piston disposed for reciprocation in said combustion cylinder, and a guide shaft axially arranged with respect to said pistons and to which said pistons are fixed, a cylinder head mounted on the outer end of each said compressor cylinder and having a bearing therein supporting said guide shaft, a frame mounted on the inner end of each said compressor cylinder and supporting said combustion cylinder, said frame also having a bearing therein supporting said guide shaft for reciprocal movement, a cylindrical member carried by each said frame and extending into the adjacent end of said combustion cylinder, each said cylindrical member having an exterior surface in spaced relation to the opposed interior surface portion of said combustion cylinder to provide an annular chamber therebetween, said power piston having a skirt reciprocally receivable in said annular chamber to compress air therein, said annular chamber thereby constituting a bounce chamber.

16. A free piston machine comprising a rigid frame including a pair of axially aligned compressor cylinders and a combustion cylinder between said compressor cylinders, a pair of piston assemblies each having a compressor piston disposed for reciprocation in one of said compressor cylinders and a power piston of a diameter not larger than that of said compressor piston disposed for reciprocation in said combustion cylinder, each said power piston. having a crown, and means supporting said piston assemblies for reciprocal movement comprising two guide shaft parts axially arranged with respect to said piston assemblies, a pair of spaced bearings engaging each said guide shaft part for reciprocal movement thereof in said bearings, a separate support ixed to said frame and carrying each said bearing, each said piston assembly being iixed to one of said guide shaft parts with said compressor piston being disposed between said pair of spaced bearings, each said piston assembly being completely and solely supported by a respective pair of said supports whereby said cylinders are free of piston assembly load and side thrust, each said guide shaft part extending through one of said compressor pistons and into the crown of one of said power pistons, and a member closing each end of said combustion cylinder and through which one of said guide shafts extends, each said member being carried by one of said supports and having mounted therein one of said bearings.

17. A free piston machine comprising a rigid frame including a pair of axially aligned compressor cylinders and a combustion cylinder between said compressor cylinders, a pair of piston assemblies each having a compressor piston disposed for reciprocation in one of said compressor cylinders and a power piston of a diameter not larger than that of said compressor piston disposed for reciprocation in said combustion cylinder, and means supporting each said piston assembly for reciprocal movement comprising a guide shaft iixed to said piston assembly and axially arranged with respect thereto, a pair of spaced, separate supports ixed to said frame and carrying each said guide shaft for reciprocal movement thereof in said supports, each said piston assembly being completely and solely supported by a respective pair of said supports whereby said cylinders are free of piston assembly load and side thrust, each said compressor piston being disposed between a pair of said supports, one support of each said pair thereof constituting a member closing an end of said combustion cylinder.

References Cited in the le of this patent UNITED STATES PATENTS 758,801 Wilhelmi May 3, 1904 2,079,289 Jancke May 4, 1937 2,425,375 Kilchenmann Aug. 12, 1947 2,461,224 Meitzler Feb. 8, 1949 2,494,573 Mueller Jan. 17, 1,950 2,869,524 Spier Ian. 20, 1959 2,878,990 Zurcher Mar. 24, 1959 FOREIGN PATENTS 53,523 Denmark Aug. 30, 1937 768,155 France Aug. 1, 1934 625,741 Germany Feb. 15, 1936 557,206 Great Britain Nov. 10, 1943 199,017 Switzerland Iuly 15, 1935 

1. A FREE PISTON MACHINE COMPRISING A RIGID FRAME INCLUDING A PAIR OF AXIALLY ALIGNED COMPRESSOR CYLINDERS AND A COMBUSTION CYLINDER BETWEEN SAID COMPRESSOR CYLINDERS, A PAIR OF PISTON ASSEMBLIES EACH HAVING A COMPRESSOR PISTON DISPOSED FOR RECIPROCATION IN ONE OF SAID COMPRESSOR CYLINDERS AND A POWER PISTON OF A DIAMETER NOT LARGER THAN THAT OF SAID COMPRESSOR PISTON DISPOSED FOR RECIPROCATION IN SAID COMBUSTION CYLINDER, EACH SAID POWER PISTON HAVING A CROWN, AND MEANS SUPPORTING SAID PISTON ASSEMBLIES FOR RECIPROCAL MOVEMENT COMPRISING TWO GUIDE SHAFT PARTS AXIALLY ARRANGED WITH RESPECT TO SAID PISTON ASSEMBLIES, A PAIR OF SPACED BEARINGS ENGAGING EACH SAID GUIDE SHAFT PART OF RECIPROCAL MOVEMENT THEREOF IN SAID BEARINGS, A SEPARATE SUPPORT FIXED TO SAID FRAME AND CARRYING EACH SAID BEARING, EACH SAID PISTON ASSEMBLY BEING FIXED TO ONE OF SAID GUIDE SHAFT PARTS WITH SAID COMPRESSOR PISTON BEING DISPOSED BETWEEN SAID PAIR OF SPACED BEARINGS, EACH SAID GUIDE SHAFT PART EXTENDING THROUGH ONE OF SAID COMPRESSOR PISTONS AND INTO THE CROWN OF ONE OF SAID POWER PISTONS, AND A CYLINDRICAL MEMBER PROJECTING AXIALLY INTO EACH END OF SAID COMBUSTION CYLINDER, EACH SAID CYLINDRICAL MEMBER BEING CARRIED BY ONE OF SAID SUPPORTS AND HAVING MOUNTED THERIN ONE OF SAID BEARINGS, EACH SAID CYLINDERICAL MEMBER HAVING AN EXTERIOR CYLINDRICAL SURFACE IN RADIALLY SPACED RELATION TO THE OPPOSED CYLINDRICAL INTERIOR SURFACE PORTION OF SAID COMBUSTION CYLINDER TO PROVIDE AN ANNULAR CHAMBER THEREBETWEEN, EACH SAID POWER PISTON HAVING A SKIRT RECIPROCALLY RECEIVABLE IN ONE OF SAID ANNULAR CHAMBERS TO COMPRESS AIR THEREIN, EACH SAID ANNULAR CHAMBER THEREBY CONSTITUTING A BOUNCE CHAMBER. 